Entropy and entropy production have recently become mathematical tools
for kinetic and hydrodynamic limits, when deriving the macroscopic
behaviour of systems from the interaction dynamics of their many
microscopic elementary constituents at the atomic or molecular level.
During a special semester on Hydrodynamic Limits at the Centre Émile
Borel in Paris, 2001 two of the research courses were held by C. Villani
and F. Rezakhanlou. Both illustrate the major role of entropy and
entropy production in a mutual and complementary manner and have been
written up and updated for joint publication. Villani describes the
mathematical theory of convergence to equilibrium for the Boltzmann
equation and its relation to various problems and fields, including
information theory, logarithmic Sobolev inequalities and fluid
mechanics. Rezakhanlou discusses four conjectures for the kinetic
behaviour of the hard sphere models and formulates four stochastic
variations of this model, also reviewing known results for these.